U.S. Pat. No. 6,570,584 discloses an OLED display device with more than the conventional red, green, and blue sub-pixels. The additional sub-pixel may have a color selected outside the color gamut possible with the red, green, and blue sub-pixels to obtain a wider color gamut. The display system uses a conventional RGB input signal to create an appropriate multi-color signal for driving all the sub-pixels. Alternatively, the additional sub-pixel may have a color inside the color gamut possible with the red, green, and blue sub-pixels to increase the efficiency and lifetime of the display.
A color data transformation circuit converts the input signal to values necessary for controlling each of the sub-pixels. The transformation circuit calculates the appropriate amounts of light from each of the three available sub-pixel colors to reproduce the desired color at each of the four sub-pixels using well known matrix transforms or lookup tables. The amount of light produced by a sub-pixel depends on a numerical value supplied to the sub-pixel. The numerical value is, for example an eight or six bit value. In general, many different possibilities exist to transform the input signal to the drive values of the sub-pixels.
A transformation circuit which performs matrix transformations has the drawback that a lot of matrix multiplications are required. Either an expensive and fast calculation circuit is required or an algorithm has to be constructed to pre-calculate the majority of the computationally intensive mathematical calculations to enable real time operation. A pre-calculation and a transformation circuit which uses look-up tables have the drawback that the algorithm is pre-fixed to one of the possible solutions.